Hydraulic pump and motor apparatus with load responsive pump regulating means



2,936,588 May 17, 1960 w VAN GERPEN H. HYDRAULIC PUMP AND MOTOR APPARATUS WITH LOAD RESPONSIVE PUMP REGULATING MEANS Filed Jan. 20, 1958 INVENTOR. H. W. VAN GERPEN United States Patent i HYDRAULIC PUMP AND MOTOR APPARATUS WITH LOAD RESPONSIVE PUMP REGULATING MEANS Application January 20, 1958, Serial No. 710,145

7 Claims. (CI. 60-52) This invention relates to hydraulic apparatus and more particularly to means for controlling the output of a vari able-displacement pump.

The invention has for a principal object the provision of a pilot pump, preferablyof the constant-displacement variety, operative to impress a pilot pressure on a regulating or control valve for controlling the regulating means of a variable-displacement pump so that when the variable-displacement pump is used with a hydraulic system its output will be responsive'to a signal given by the system according to the load encountered thereby. A feature of the use of the constant-displacement pilot'pump is that the pressure created thereby may be relatively low and the larger variable-displacement pump can have its output cut back to a minimum when the hydraulic system is inactive. A further feature of the inventionresides in the ability of the arrangement to adapt itself to a variable-displacement pump of the type in which the regulating control is imposed on the pistons of the pump itself, as distinguished from varying eccentricity of a rotor as is common in the prior art.

The foregoing and other important objects and desirable features inherent in and encompassed by the invention will become apparent as a preferred embodiment thereof is disclosed by way of example in the ensuing specification and accompanying sheet of drawings wherein the single figure illustrates schematically and partly in section an arrangement involving a variable-displacement pump, a constant-displacement pilot pump and a hydraulic system, together with demand valve means for coordinating the apparatus. i The numeral 10 represents a variable-displacement pump havingan eccentric 12 and a pair of diametrically opposed pumping pistons 14 connected through appropriate one-way valves 16 to an intake line 18 and further including output chambers 20 which lead via typical oneway valves 22 to a discharge line 24. This line is connected to a hydraulic system 26 which incorporates a control valve 28 and a motor 30 activated and deactivated by the control valve. The line 18 is connected toreservoir at R. The control valve is shown schematically and is .of the closed center type, being connected at one side to the discharge line 24 and alternately to reservoir at 32. The other side of the valve is connected by apair of motor lines 34 to opposite ends of the motor 30.

The pump regulating device, by means of which the 2,936,588 Patented May 17, 1960:

ICC

otherwise, the pistons would operate at only part stroke. Accordingly, the means for returning the pumping pistons includes the regulating devices 36-38 and fluid in vary; ing amounts is supplied to the manifold 40 to vary the extent to which the regulating pistons 36 will push their respective pumping pistons back on the respective intake strokes. That is to say, and assuming that the manifold 40 contains a fixed volume of fluid, it will be seen that as one piston 14 moves out, its piston 36 will force fluid from its chamber 38 to the chamber 38 of the opposite piston 36 and this in turn will cause the opposite piston 14 to move in on its intake stroke. By varying the volume of fluid in the manifold, the intake stroke may be regulated between a predetermined minimum and a predetermined maximum. Accordingly, pump output at the discharge line 24 can be similarly regulated.

Regulation depends in the first instance upon the automatic actuation of demand valve means 42, here comprising a valve housing 44 having a bore 46 in which a valve spool 48 is axially 'shiftable. Biasing means in the form of a spring 50 acts on one piston portion 52 of the spool 48 to shift the spool to the left as seen in the drawings. A second piston portion 54 on the spool is receivable of fluid pressure so that the spool 48 can shift to the right against the spring 50.

A constant displacement pump 56 has its intake 58 connected to reservoir at 60 and has its: high-pressure side or line 62 normally closed by a relief valve 64. In

the apparatus described, the relief valve setting at 64 is relatively low; for example, 200 p.s.i. A pilot line,66 is connected to the high-pressure line 62 upstream of the relief valve 64 and leads across the valve housing 44 of the demand valve means 42 to a permanent connection at 68 with the discharge line 24 of the variable displacement pump 10. A one-way or non-return valve 70 is interposed in the pilot line to prevent reverse flow from the discharge line 24 to the pilot line 66. The design of the valve spool 48 is such that the pilot line is never interrupted. The spring acting on the non-return valve 70 is relatively light, sufficient only to keep the ball normally in place.

The varying volume of fluid supplied to the manifold 40 is taken from the high-pressure line 62 via an input line 72 and the pilot line 66, the valve housing 44having axially spaced apart ports 74; and 76 controllable by the piston portion 54 on the valve spool'48. In brief, when output of the pump is increased and reduced, takes the form of a pair of regulating pistons 36 fixed coaxially respectively to the pumping pistons 14. Each piston 36 operates in a' regulating chamber 38 and these' chambers are interconnected by a manifold 40. The operational characteristics of the pump 10 are such that inertia and These forces conreturning the pumping pistons on their intake strokes;

the valve spool 48 moves to the right, it can cut off the port 76, thus discontinuing flow to the line 72 and manifold 40 while permitting flow through the: pilot line 66 to the discharge line 24 past the valve 78. The line 72, and consequently the manifold 40, is bled to reservoir at 78 via a properly calibrated orifice 80.

A passage or conduit 82 connects the variabledisplacement discharge line 24 to the bore 46 of the demand valve means 42 atthe piston 54 ofthe spool 48. The opposite end of the valve bore 46 is connect-ed by a signal line.84 to the hydraulic system 26, as by a pair of signal line branches 86 having one-way check valves 88 therein and being-bled to reservoir at 90 via an orifice 92. The signal line branches 86 are connected to the motor lines 34 between the motor and the control valve 28. When the control valve 28 is closed, there is noflow or pressure in the signal line 84, since any fluid trapped therein will have escaped to reservoir at 90 via the orifice 92. When the apparatus is idle, the spring 50 will keep the spool 48 to the position shown.

The two pumps 10 and 56 are preferably geared together or otherwise driven in unison. When they are started, the pressure in the high-pressure line 62 will of course reach the setting of the relief valve 64 and since the highpressure line is co n at 6- 8 t the variable-displacement discharge line 24, a similar pressure, at least, will exist in the conduit 82, acting against.

have a force of 150 lbs., and the piston 54 will therefore cut off the port 76 so that the volume of fluid hr the manifold 40 via 72 will be relatively low, since it can escape to reservoir at 80-78. v

The foregoing assumes that the: control valve 28 i closed. If, so, then there is no requirement for high output from the variable-displacement pump 10, which is consistent. with the reduction in fluid in the manifold 40 and consequently in the regulating device chamhers. 38. As the eccentric 12 rotates and causes the pumping'pistons 14 to tend to stay toward the outer ends of their strokes, the output of this pump will be relatively low.

When the control valve 28 is moved to one or the other of its active positions, flow and pressure occur in the discharge line 24, as Well as in the activated motor line and also in the signal line 84 and the load pressure in the activated motor line 34 will transmit a signal through the associated signal branch 86 to the signal line 84. That is to say, the pressure at both sides of the control valve 28 will now be the same and the signal pressure at 84 will act in aid of the spring 50 to assure that the valve spool 48 moves to the left. In other words, opening of the control valve 28 indicates that the system 26 is activated and accordingly it imposes a hydraulic demand on the variable-displacement pump 10. The demand valve 42 makes the necessary corrections to enable increase in the output of the pump to satisfy this demand When the port 76 is opened, the high-pressure line via 667476 supplies fluid to the line '72 and to the manifold 40, thus flowing to the chambers 38 and overcoming the operational bias on the pumping pistons 14 so that these pistons are returned fully, for example, on their intake strokes. Since the pumping pistons now have full intake strokes and are positively driven on their discharge strokes the output in the discharge line 24 will be at a maximum. =For present purposes, let it be assumed that this pressure is 900 p.s.i. As the load encountered by the motor 30 begins to move, there will be a pressure drop across the valve 28, with the result that the pressure at 84 will be less than that at 82, and the valve spool 48 will tend to move to the right against the spring 50, cutting ofl the port '76. As long as the demand in the system can be satisfied by'the pump 10, the valve spool 48 will control the port 76 to maintain the output at that requirement. If the demand falls off, the pressure at 84 will fall off and the valve spool 48 can increase itsrestricting effect on the port 76. If the. demand increases, pressure at 84' increases and shifts the valve spool 48 to the left, increasing opening of the port 76 *and thereby increasing the supply of fluid to the manifold 40. As will be clear, as long as the supply at 76 equals the loss at 80-78, the volume in the manifold is constant.

The one-way valve 70 prevents high discharge line pressure from escaping to the high-pressure line of the pump 56 and thence past the relatively light relief valve 64.

In the event of a sudden pressure increase in the discharge line 24, the valve spool 48 will shift a maximum distance to the right, and will uncover a relief valve line 94 which leads to reservoir at 96.

. 4i 86 prevent signal flow from one branch to the other. In the. event. that the motor isv used. in situationsv in which it will be subjected to residual load when the control valve 28 is closed, it is desirable to employ hydraulically operated check valves in the motor lines to prevent the residual load from creating. pressure in the signal line branches. 1

On the basis of the foregoing disclosure, many varia-- tions: will occur to those versed in the art. Thesemay be easily achieved without departing from the spirit and scope of the invention.

What is claimed is: V

1. Hydraulic apparatus, comprising: a variable-displacement pump having a discharge line; pump Output regulating means biased to reduce pump output to a selected minimum and fluid pressurizible to increase pump output up to a selected maximum; a hydrau-v lic system connected to the discharge line and ineluding a motor and a motor control valve changeable between static and operating conditions to incur variations in system demand on the pump; a fluid pressure source other than the pump and having a supply line connected to the regulating means; demand valve means operative to open and close the supply line to respectivily incur pressurizing and depressurizing of the regulating means for respectively increasing and decreasing. pump output; means biasing the demand valve means to open the. supply line; first piston means acting on the demand valve means in opposition to the biasing means and receivable of discharge line pressure at or above a predetermined value to incur closing of the supply line; a pilot line connected between the source and the discharge line upstream of the motor control valve for pressurizing the discharge line at said value; a one-way valve in the pilot line for preventing reverse flow to the source; and second piston means acting on the demand valve means in aid of the biasing means and receivable of pressure increases in the system when said system is operative so that the demand valve means opens and closes the supply line in accordance with system demand. and thereby regulates pump output according to system demand.

2. The invention defined in claim 1, including: means affording a relief port normally closed by the demand valve means and openable by excess. discharge line. pres-.- sure acting on the first piston means. 7

3. Hydraulic apparatus, comprising: a variable-displacement pump having a discharge line; pump output regulating means biased to reduce pump output to a selected' minimum and fluid pressurizible to increaseipump output up to a selected maximum; a fluid pressure source other than the pump and having a supply line connected tothe regulating means; demand valve means operative to open and close the supply line to respecively incur pressurizing and depressun'zing of the regulating means for respectively increasing and decreasing pump output; and means responsive to variations in pressure in the discharge line for opening and closing the supply line by the demand valve means to respectively increase and decrease pump output as discharge line pressure increases and decreases. 7

4. The invention defined in claim 3 including: means aflording a relief port normally closed by the demand valve means and openable by excess discharge line pressure acting on the demand valve means.

5. Hydraulic apparatus, comprising: a variable-displacement pump having a discharge line; pump output regulating means biased to reduce pump output to a selected minimum and fluid pressurizible to increase pump output up to a selected. maximum; a hydraulic system connected to the discharge line and including a motor and a.- motor control valve changeable betweenstatic and operating conditions to incur variations in system demand on the pump; a fluid pressure source other than the pump and having a supply line connected to the regulating means; demand valve means operative to open and close the supply line to respectively incur pressurizing and depressurizing of the regulating means for respectively increasing and decreasing pump output; means biasing the demand valve means to open the supply line; first piston means acting on the demand valve means in opposition to the biasing means and receivable of discharge line pressure at or above a predetermined value to incur closing of the supply line; and second piston means acting on the demand valve means in aid of the biasing means and rccievable of pressure increases in the sysem When said system is operative so that the demand valve means opens and closes the supply line in accordance with system demand and thereby regulates pump output according to system demand.

6. Hydraulic apparatus, comprising: a variable-displacement pump having a discharge line and a plurality of pumping elements consecutively reciprocable to apply pump output to said line, each element being movable on intake and discharge strokes of predetermined length and operationally biased toward the end of the discharge stroke; means operative variably to overcome the bias and including a fluid manifold having a plurality of chambers and a plurality of pistons respectively in the chambers and connected respectively to the elements; a hydraulic system connected to the discharge line and including a motor and a motor control valve changeable between static and operating conditions to incur variations in system demand on the pump; a fluid pressure source other than the pump and having a supply line conmeans to open the supply line; first piston means acting on,

the demand valve means in opposition to the biasing means and receivable of discharge line pressure at or above a predetermined value to incur closing of the supply line; and second piston means acting on the demand valve means in aid of the biasing means and receivable of pressure increases in the system whensaid system is operative so that the demand valve means opens and closes the supply line in accordance with system demand and thereby regulates pump output according to system demand.

7. The invention defined in claim 6, including a pilot line conneced between the source and the discharge line upstream of the motor control valve for pressurizing the discharge line at said predetermined value; and a oneway valve in the pilot line for preventing reverse flow to the source.

References Cited in the file c-f this patent UNITED STATES PATENTS 

